(1) Field of the Invention
This invention relates to an image handling device, wherein an image of a document placed on a glass document table is optically read and is projected onto a device for electrically retaining the image, especially to a device for detecting such document conditions as size and density of the image. (Density means darkness of the color hereinafter.)
(2) Description of the Related Art
In order to read a document image in an image forming apparatus as an example of such an image handling device, the document size and the density of the image ought to be detected for the purpose of determining the scanning area and the quantity of light. The followings are some examples of conventional methods for detecting the document size.
(1) Pre-scanning is conducted by a CCD for reading a document image. This method has the problems that pre-scanning prolongs the whole copying operation and that the document size cannot be detected unless the rear surface of a document holding cover has a different color from that of the document.
(2) A special sensor for detecting the document size is provided below a glass document table. One construction of this method is as follows. A sensor supporting arm, comprising two rods connected to each other with a pin, is equipped with a plurality of sensors and is connected to a scanner at one end thereof. The document size is detected by pivoting the two rods. Practically, when the scanner stops at the scan completing position, the sensor supporting arm is pivoted into a V shape. The on/off state of each sensor indicates whether there is a document in its detecting spot or not, and the detection results of all the sensors are computed, whereby the document size is found. When the scanner starts scanning and reaches its destination, the sensor supporting arm is folded into two along one end of the glass document table in its longitudinal direction. Although this method does not require pre-scanning and so shortens the whole copying operation, it involves the following problems. The connecting section of the sensor supporting arm and the scanner is inevitably complicated and also have to be highly accurate. Therefore, a lot of parts are required, which increases the size of the device, the production cost, and difficulty in processing, assembling and operation. Further, the load of a motor for driving the scanner is increased.